The present invention relates to a metal cord suitable for being used as a reinforecment for rubber products such as tires and, more particularly, it relates to a metal cord with a double-layered structure.
Metal cords such as steel cords, for example, which have been conventionally used as reinforcements for rubber products such as tires, for example, are of the single-layered strand type, multi-layered strand type, complex (or cable) type, or the like, and these are made by stranding wires each having a diameter of about 0.15 mm to 0.38 mm. The wires which form these cords are usually stranded to closely contact one another, and the cords thus formed can be called the compact type.
In the case of the conventional cords of the compact type, the wires closely contact one another, as described above. Even when they are used for reinforcing rubber products, therefore, rubber cannot enter them but only cover their surface. In a case where damage occurs to the rubber portion of the rubber product and reaches the cord therein, for example, in reinforced rubber products such as tires, water reaches the inside of the cord through this damaged portion to corrode the wires, or finally break the tire itself.
In order to overcome this drawback, U.S. Pat. No. 4,258,543 discloses a metal cord of the single strand type wherein wires are separated from one another to become larger than the outer diameter of the cord of the compact type. Further, U.S. Pat. No. 4,022,009 discloses a cable constructed by aligning plural wires parallel to one another, stranding the whole of these aligned wires at a long pitch to form a core, and winding a wire around this core. In the case of these cords and cables disclosed by U.S. Patents, the wires relatively loosely contact one another. Therefore, rubber can easily enter the wires, thereby enabling the rubber product to be reinforced and the wires to be sufficiently enclosed by rubber. However, these cords are relatively unstable in construction and inferior in durability.